Thermal crack formation in TiCN/α-Al2O3 bilayer coatings grown by thermal CVD on WC-Co substrates with varied Co content

Rafael Panayiotis Stylianou, Dino Velic, Werner Daves, Werner Ecker, Michael Tkadletz, Nina Schalk, Christoph Czettl, Christian Mitterer

Publikation: Beitrag in FachzeitschriftArtikelForschungBegutachtung

11 Zitate (Scopus)

Abstract

Within this work, the thermal stress build-up of chemically vapor deposited TiCN/α-Al 2O 3 bilayer coatings was controlled by tuning the coefficient of thermal expansion (CTE) of the substrate material. This was implemented through a Co content variation from 6 to 15 wt.% in WC-Co substrates, which exhibit higher CTEs with increasing Co contents and thereby approach the CTE values of TiCN and α-Al 2O 3. High temperature X-ray diffraction was employed to determine thermal expansion of an α-Al 2O 3 powder. Crystallographic texture of the α-Al 2O 3 coating layer was evaluated by electron backscatter diffraction and taken into consideration in order to assign the appropriate in-plane CTE. This consideration indicated a lower CTE mismatch of α-Al 2O 3 with WC-Co, compared to TiCN with WC-Co. X-ray diffraction was further utilized for the determination of residual stress in TiCN and α-Al 2O 3, demonstrating a decrease in both layers for Co contents below 12.5 wt.%. Decreasing stress signaled the formation of thermal crack networks confirmed by scanning electron microscopy surface images. Lower residual stresses were determined in TiCN compared to α-Al 2O 3 layers of bilayer coatings, contradicting finite element simulations of thermo-elastic stress, that were carried out to illustrate the stress relaxation effects caused by thermal cracks. Monolayer TiCN coatings were annealed at 1000 °C, to replicate stress relaxation taking place during α-Al 2O 3 deposition, exhibiting a similar residual stress state to TiCN base layers of bilayer coatings. Thermal crack formation was found to be the dominating stress relaxation mechanism in α-Al 2O 3, while TiCN undergoes further relaxation through secondary mechanisms.

OriginalspracheEnglisch
Aufsatznummer125687
Seitenumfang11
FachzeitschriftSurface & coatings technology
Jahrgang392.2020
Ausgabenummer25 June
Frühes Online-Datum21 Apr. 2020
DOIs
PublikationsstatusVeröffentlicht - 25 Juni 2020

Bibliographische Notiz

Funding Information:
The authors would like to express their appreciation towards Dr. Christian Saringer for the insightful discussions and Dipl.-Ing. Christoph Kickinger for providing high temperature X-ray diffraction data of the α-Al 2 O 3 powder. The Austrian Federal Ministry for Digital and Economic Affairs and the National Foundation for Research, Technology and Development , in addition to the Austrian Research Promotion Agency (FFG) within the framework of the EOC 4 T project (grant number: 853857 ), are gratefully acknowledged for financially supporting this research. The authors also gratefully acknowledge financial support from programs of the COMET-K2 competence centers within the framework of the IC-MPPE project (grant number: 859480). This project is supported by the Austrian Federal Ministries for Transport, Innovation and Technology (BMVIT) and for Digital and Economic Affairs (BMDW), represented by the Austrian Research Promotion Agency (FFG), and the federal states of Styria , Upper Austria and Tyrol .

Publisher Copyright:
© 2020 Elsevier B.V.

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